Filaments wet-spun from viscosity-stabilized aromatic polyamides

ABSTRACT

Aromatic polyamides are advantageously viscosity-stabilized by the presence during polymerization of a stabilizing amount of a compound of   WHEREIN R is hydrogen, a lower alkyl radical or an aryl radical. The inherent viscosity of the polyamide is in the range of 0.8 and 2.4. Filaments wet-spun from such polyamide show improved tensile strength and resistance to abrasion.

United States Patent I Ralph W. Smith Gull Breeze, Fla. 785,370

Dec. 19, 1968 Dec. 14, 1971 Monsanto Company St. louis, Mo.

[72] Inventor [21 1 Appl. No. [22] Filed [45 1 Patented [73} Assignee [54] FILAMENTS WET-SPUN FROM VISCOSITY- STABILIZED AROMATIC POLYAMIDES 32.6 N, 78 R; 264/210 F [56] References Cited UNITED STATES PATENTS 3,049,5 l 8 8/1962 Stephens 260/78 Primary Examiner-Donald E. Czaja Assistant ExaminerV. P. Hoke Attorneys-Stanley M. Tarter and John W. Whisler ABSTRACT: Aromatic polyamides are advantageously viscosity-stabilized by the presence during polymerization of a zinss 9 mv 3 29994in? was? wherein R is hydrogen, a lower alkyl radical or an aryl radical. The inherent viscosity of the polyamide is in the range of 0.8 and 2.4. Filaments wet-spun from such polyamide show improved tensile strength and resistance to abrasion.

FILAMEN'IS WET-SPUN FROM VISCOSITY-STABILIZED AROMATIC POLYAMIDES BACKGROUND OF THE INVENTION prepared by heating certain amino acids or by heating certain diamines with dibasic carboxylic acids under polyamidation 1 conditions. Aliphatic polyamides produced from polymers of 6aminocaproic acid and polymers of hexamethylene diamine and adipic acid have found wide spread acceptance in the textile industry. Commonly these polymers are referred to as nylon-6 and nylon-66, rspectively.

These polyamides have melting points normally above 200 C. but below,280 C. For most textile purposes these melting points are quite acceptable. However, with the advent of use of fibers in the aerospace activities and other areas where extraordinary hot environment is present, filaments haying much higher melting points were required. To meet this need wholly aromatic polyamide strands have been produced. While the aliphatic polyamides can be spun by the melt spinning process, the so-called wholly aromatic polyamides have such a high melting point that in order to produce filaments therefrom one must resort to using the wet spinning process with its attending disadvantages.

As is well known wet spinning involves dissolving the polymer in a suitable solvent and extruding the resulting solution in a coagulation bath wherein the polymer precipitates as filaments and the solvent is extracted from the extruded streams. It was found that by using solutions of aromatic polymer, solvent removal during wet spinning was encountered with much difiiculty. It was noted that during coagulation a rather impervious skin developed on the forming filaments. This presence of skin hindered solvent removal from the innner core of the filaments. The filaments were low in tensile strength and abraded easily during use.

SUMMARY OF THE INVENTION An aromatic polyamide having been viscosity-stabilized with a small amount of a compound of the formula:

DETAILED DESCRIPTION It has been found that aromatic polyamide strands of improved strength and abrasion resistance can be obtained by preparing such polyamides in the presence of a small amount of certain formamides whose chemical formulas have been structurally presented above, generally in the range of 0.204-1 .63 percent based on the weight of the polymer. However, it has been found that fibrids useful in the manufacture of dielectric paper and composite materials can be formed more readily by including formamides in the range above L63 percent up to 4.0 percent by weight of the polymer. Tensile strength in the range of 5-8 grams per denier are obtainable when the end uses of the strands require strength. It is also possible that the strength be 1-5 grams per denier for end uses not requiring better tensile properties.

The polyamide useful in the practice of the invention is referred to herein as aromatic polyamides. This term refers to polymers wherein repeating units are linked together by a carbonamide group, i.e., the radical:

The amine and the carbonyl of each repeating carbonamide radical is directly attached to a carbon atom in the ring of an aromatic radical. The term aromatic radical means a carbocyclic ring possessing resonance. Thus included are all resonance-stabilized ring systems whether benzene-aromatic or hetero-aromatic. They may be single, multiple or fused ring structures. Exemplary aromatic radicals are in which R is preferably a lower alkyl, lower alkoxy or halogen, n is a number from 0-4 inclusive, and X is preferably one of the groups 0 r r -p-, -0-, -sor -opoly-N,N-m-phenylenebls(m-benzamide)4,4-blpheny1dicarbonam1de atom elected from the group of chlorine, bromine and iodine, the first mentioned halogen being preferred, is added to the I-H H H diamine solution along with a sufficient amount of proton acg l ceptor and the mixture stirred continuously until the reaction 5 is complete, the time depending upon the type of polymerization system and the polymer being prepared. Reaction is generally complete within a few minutes to a few hours. 0 Before the reaction is complete and preferably before the L g reaction is initiated the formamide viscosity stabilizer is added. Representative examples of specific fonnamide suita- 1 ble for purpose of this invention are formamide; N-methyl-formamide; n,N-dimethylformamide (the most preferred); N- ethylformamide; N,N-diethylformamide; N-methyl-N-ethylpoly-4,4-bls(p-aminophenyl)-2,2'-blthiazo1elsophthalamlde l5 formamide; l -p py y -P y H N i4: H formamide; and others.

I 1 1 The amount of formamide stabilizer employed is critical Q fi and determines the ultimate spinning and fiber properties of H-C--i; iJ-b-1-1 the product. When the aromatic polyamide is to be employed y for making filaments and the like quantities of formamide stabilizer should be at least 0.204 percent and nonnally not in exf l cess of 1.63 percent by weight based on the weight of the cpolymer. The preferred range is 0.53 percent to 1.22 percent.

J Below 0.204 percent the viscosity of the polyamide is not appreciably affected with'the result that the advantages of the present invention are not utilized to the fullest extent. Wet r poly-2,5-bis(pamlnophenyl) -1,3,4-oxadlazo1e lsophthalamlde :11;:2: :32: 8 2 ;ff fil i ggi lxz ig i 0 abrasion resistance. if used in excess of 1.63 percent, the for- Q g mamide stabilized aromatic polyamides are not suitable for w L, fiber-forming material but may be used for film and coating material. When used in excess of 2.55 percent, the

polymerization of the material has been so limited that the poly 3'4l diaminobenzanilide isophthalamide polymer has substantially no known utility except perhaps as a 35 yarn sizing ingredient. The viscosity of the polymer IS related E' to the amount of stabilizer added. Where dimethylformamide fit o H H 0 N JL QJIJE is employed in an amount of 0.204 to 1.63 percent, the inl- J herent viscosity of-the polymer is about 1 .652.4. For amounts of 0.53-122 percent the inherent viscosity is 1.8-2.2. And

d -4,4'.di ih 51 terephihalamide polyamide has an inherent viscosity of only 1.4. Inherent Iherent viscosity is determined in accordance with the following equation.

1 FR 0 I H H o o-l l kn g lx il g g 1; inh (inherent viscosity) lnnrel/C L v The relative viscosity (-qrel) is determined by dividing the flow w W time in a capillary viscometer of a dilute solution of the The process of preparing the polymer of the invention is conpolymer by the flow time for the pure solvent. The concentraveniently conducted by known interfacial or solution polycontion (C) is generally 0.5 gram of polymer per 100 ml. of S ludcnsation technique. The latter is preferred and involves distion. The measurements are made at 22 C. in N,N- solving a wholly aromatic diamine of the formula dintethylacetamide containing 5 percent lithium chloride.

H,N-Ar(Y),,Nl-l, where Y is selected from EXAMPLE I a. COHNAr-NHCOArand into a three liter polymerization vessel equipped with an efb. NHCOAr-COHNArficient agitator, inert gas bleed device, and a drying tube were where Ar is an aromatic radical of six through 16 carbon placed 209 grams of rn-phenylene bis-(m-aminobenzamide) atoms and n is 0 to l inclusive, in a suitable solvent substanand 57 grams calcium carbonate. The vessel was flushed with tially inert to the polymerization reaction. Among such sol-- nitrogen gas. To this mixture was added 1,300 ml. of high purivents are NiN'dimethylacemmidee y 'py 60 ty N,N-dimethylacetamide containing 0.03 percent dimethyll,5-d methyl-2-pyrrolidone, hexamethylphosphol'a formamide (0.122 percent based on the weight of the rendered gficcuve m many insmnces polymer). The resulting mixture was stirred until solution of by E them a small amount l 10 i f! the diamine was effected and was cooled to -20 C. by means trg za iz gi izg fii js s lgxgggfia t xmzz of a dry ice and acetone bath. Agitation was again started and 122 grams of purified terephthaloyl chloride was added. As

chloride or calcium chloride. The preferred solvents for solud m on polymerization are N'Ndimethllacemmide or the viscosity and temperature gradually increase e stirrer dimethylacetarnide containing 5 percent lithium chloride. The was decreafwd to provide Proper ixing' The temperature f the sglution is lowered to between plus e chloride of reaction was neutralized with the added calcium minus 20 and an aromatic diacid halide of the formula: 0 carbonate by raising the reaction temperature to 80 C. The

inherent viscosity of the polymer was determined to be 2.50.

The polymer containing solution was pumped with some I difficulty through a multihole spinneret submerged in an aqueous spin bath. The resulting filaments were withdrawn from wherein Ar is divalent aromatic radical and Hal is a halogen the bath and subjected to after treating steps of washing. draw- 40 when 2.55 percent dimethylformamide is used, the aromatic.

EXAMPLE [I Example 1 was repeated with the exception that the dimethylacetamide solvent contained 0.30 percent N,N- dimethylformamide (1.22 percent based on polymer weight).

,The polymer had an inherent viscosity of 1.84. It was found that fabric made from the wet spun resulting filaments had improved strength of 5.8 g./d at 16 percent break elongation and improved abrasion resistance. Microscopic analysis of the yarn showed a less pronounced skin-core effect.

EXAMPLE Ill Example 1 was repeated with the exception that N,N- dimethylformamide was added to increase the concentration to 0.60 percent. The polymer had an inherent viscosity of 1.44. It was found that fabric made from the resulting filaments had improved abrasion resistance. Microscopic analysis of the yarn showed a substantial absence of any skin-core effect.

EXAMPLE IV Example I was repeated with the exception that the solvent contained 0.48 percent N,N-dimethylformamide. The resulting polymer had an inherent viscosity of 1.79. It was again found that fabric made from the resulting wet-spun filaments had excellent abrasion resistance.

EXAMPLE V Example I was repeated with the exception that the solvent contained only 0.01 percent N,N-dimethylformamide (0.04 percent based on polymer weight). The resulting polymer had an inherent viscosity of 2.36. Difficulty was encountered in extruding the polymer solution to form fibers because of the occurrence of gelatinous polymeric particles. It was again found that fabric made therefrom had unsatisfactory resistance to abrasion.

EXAMPLE Vl Into the apparatus described in example I were placed 104.5 grams of m-phenylene bis(m-aminobenzamide) and 650 ml. of high purity N,N-dimethylacetamide. Calcium carbonate, 28.6 grams, was added and the mixture was cooled to 20 C. Just prior to the addition of 60.9 grams of the terephthaloyl chloride, 4.0 grams of formamide was added. The aromatic diacidehloride was then added and the polymerization was completed as described in example 1. It was found that the presence of the dimethylacetamide efiectively regulated the molecular weight of the polymer.

Likewise, when other aromatic polyamides are prepared in the presence of a suitable amount of other fonnamides within the scope of the present invention, one produces polymers having reduced inherent viscosity. Filaments made therefrom have increased tensile properties and abrasion resistance.

As can be seen, an important aspect of the present invention is the regulation of the molecular weight of aromatic polyamides by the use of relatively low cost N,N-dialkyl fonnamides. Among the advantages of regulating the molecular weight of such polyamides are: to allow the use of high solids concentrations of polymer solutions which facilitate the spinning of high-strength fibers; to prevent uncontrolled polymerization resulting in the formation of undesirable gel formations; and to control the molecular weight of the polymer within a given range so that changes in spinning variables are not needed for producing a consistently high-quality fiber.

I claim:

1. A wet-spun filament having improved tensile properties and abrasion resistance made form an aromatic polyamide viscosity-stabilized with a compound of the formula:

where R is selected from the group consisting of hydrogen, lower alkyl of one to six carbon atoms, and aryl, the inherent viscosity of the polymer being in the range of 1.65 and 2.4, the viscosity stabilizer being present during polyamidation in an amount of 0.204-l.63 percent based on the weight of the polyamide.

2. A wet-spun filament having improved tensile properties and abrasion resistance made from an aromatic polyamide of the formula wherein n is indicative of the molecular weight, viscosity-stabilized with N,N-dimethyl formamide, the inherent viscosity of the polyamide being in the range of 1.8 and 2.2, and the said formamide being present during polyamidation in an amount of 0.53422 percent based on the weight of the polyamide.

3. A wet-spun filament having improved tensile properties and abrasion resistance made from an aromatic polyamide of the fonnula wherein n is indicative of the molecular weight, viscosity-stabilized with N,N-dimethylformamide, the inherent viscosity of the polyamide being in the range of 1.8 and 2.2 and the said formamide being present during polyamidation in an amount of 0.53-1 .22 percent based on the weight of the polyamide. 

2. A wet-spun filament having improved tensile properties and abrasion resistance made from an aromatic polyamide of the formula wherein n is indicative of the molecular weight, viscosity-stabilized with N,N-dimethyl formamide, the inherent viscosity of the polyamide being in the range of 1.8 and 2.2, and the said formamide being present during polyamidation in an amount of 0.53-1.22 percent based on the weight of the polyamide.
 3. A wet-spun filament having improved tensile properties and abrasion resistance made from an aromatic polyamide of the formula wherein n is indicative of the molecular weight, viscosity-stabilized with N,N-dimethylformamide, the inherent viscosity of the polyamide being in the range of 1.8 and 2.2 and the said formamide being present during polyamidation in an amount of 0.53-1.22 percent based on the weight of the polyamide. 